In Swiss Pat. No. 517.963 (U.S. Pat. No. 3,242,664) there has already been disclosed a watch case of which the visible portions of the exterior surface exposed to contact with foreign bodies, e.g. the upper surfaces of the case in the case of a wrist watch, have an unchangeable aspect, i.e. may not be scratched by contact with such bodies, nor be oxydized or tarnish in contact with air, in a manner such that it possible to give such parts of the case a fine and well finished appearance. To arrive at this result, the cited patent proposes the employment of a layer or a solid body of sintered hard metal based on a metallic carbide, e.g. tungsten carbide or titanium carbide. The teaching provided by the cited patent has been applied since then by the present assignee to a large quantity of time pieces. These results therefrom a product highly resistant to contact with foreign bodies, this not being the case for watch cases normally manufactured of steel and which oxydize and scratch readily.
As far as the bracket of the wrist watch is concerned, Swiss patent document 632.886 proposes a series of links each covered by a rectangular platelet of hard metal and this with the purpose of forming an armour strongly resistant to attack by external agents.
The spite of the considerable impovements brought by the teachings of the two cited patents, it appears that the metallic armour formed of a metallic carbide and of which the Vickers hardness (HV) is on the order of 1400, exhibits poor resistance to certain very hard agents, e.g. silica contained in dust or in sand. To be insensitive thereto, it would appear necessary that the watch case be manufactured of a material the hardness of which at least approaches that of diamond as for example disclosed in U.S. Pat. No. 3,931,704.
As disclosed in U.S. Pat. No. 3,931,704 a watch case comprises a bottom cover and a caseband integrally formed therewith. This monoblock is made of particles of sintered diamond. However, sintering of diamonds for the volume of material considered here presents major difficulties of realization in view of the high sintering temperature and pressure required in order to obtain the desired case.